The canonical upright in the representation of object orientation

Some objects are mono-oriented, possessing a canonical or “preferred upright” orientation (Palmer at al., 1981; Jolicoeur, 1985). The implications of canonical orientations for theories of object recognition have been widely discussed (Rock, 1974; Tarr & Pinker, 1989; Ghose & Liu, 2013), but it remains unclear how “canonical” orientations fit into a theory of object orientation representation. How does the orientation representation for an object differ in canonical versus non-canonical orientations? Eight “horizontal” and 8 “vertical” objects (Fig. 1) were each presented in 16 different orientations (canonical and non-canonical) (Fig. 2). On each trial, participants (under working memory load) viewed an object in a “target” orientation and subsequently attempted to select the target from an array of that object in 16 different orientations. In previous research with poly-oriented (no preferred orientation) objects (Gregory and McCloskey, 2010), participants often selected the object primary-axis (OPA) reflection of the target: an “OPA error” (Fig 3a). We predicted that if the “uprightness” of a mono-oriented object is specifically encoded, OPA errors should be affected by canonical orientation: for canonically-oriented vertical targets, an OPA error maintains “uprightness” (Fig. 3b); for a canonically-oriented horizontal target, an OPA error would result in an “upside-down” orientation (Fig. 3c). Indeed, OPA errors were modulated by an Object type (vertical vs. horizontal) X Orientation (canonical vs. not) interaction (F(1,13) = 16.70, p< .05): for vertical objects, OPA errors were equally common for canonical and non-canonical targets (t(13) = .16, n.s.); for horizontal objects, they were significantly reduced for canonical targets (t(13) = 4.01, p< .05) (Fig. 4). Participants apparently represent the “uprightness” of a stimulus, thereby avoiding otherwise common errors that contradict this representation. These results suggest that the canonical orientation of an object affects not just the cognitive processes underlying object recognition but also those involved in representing spatial information. Meeting abstract presented at VSS 2015